Some embodiments described herein relate generally to reducing to dielectric constant of a dielectric material. More particularly, some embodiments described herein relate to printed circuit boards defining openings that reduce the effective dielectric constant of a printed circuit board substrate.
Some known electronic devices manufactured for high-speed signal transfer use printed circuit board (PCB) dielectric materials with specific characteristics. Often, such dielectric materials have a relatively high dielectric constant and can restrict the geometry of impedance-controlled strips (e.g., a transmission line such as a microstrip and/or stripline). For example, in some instances, it is desirable implement certain values of characteristic impedance of a differential pair and/or impedance-controlled strip. In such instances, the characteristic impedance of a transmission line can be mathematically described as:
      Z    0    =                    L        0                    C        0            where Z0 is the characteristic impedance of the transmission line, L0 is the inductance per unit length of the transmission line, and C0 is the capacitance per unit length of the transmission line. Furthermore, the capacitance per unit length of the transmission line for a given dielectric material can be mathematically described as:
      C    0    =      K    ⁢                  Wɛ        T            where K is a constant, W is the width of a transmission line (e.g., microstrip and/or stripline), ∈r is the relative dielectric constant of a dielectric material, and T is the thickness of the dielectric material between the transmission line and a ground reference plane.
In some known instances, the width of the impedance-controlled strips cannot be further reduced to maintain acceptable propagation losses and manufacturability. To keep the same characteristic impedance with the wider impedance-controlled strips, the thickness of the dielectric material can be increased, resulting in an increase in overall thickness of the PCB, an increase in cost, a reduction in dielectric layers, limitations in drilling, and/or other unwanted effects. Furthermore, the relatively high dielectric constant of the dielectric material increases propagation delay along the impedance-controlled strip.
Thus, a need exists for improved apparatus and methods for reducing the dielectric constant of printed circuit board dielectric material.